Currently, mobile wireless communication systems based on LTE provide broadband access to a variety of devices supporting an ever increasing number of applications, e.g., voice communications, text messaging, social applications, e-mail, web browsing, online payment, and other industrial/commercial type of applications. The traffic characteristics originating from these devices has never been more varied.
Current LTE systems are based on Orthogonal Frequency Division Multiplexing (OFDM) and therefore rely on tight control of timing of UEs to guarantee orthogonality between Single Frequency-Frequency Division Multiple Access (SC-FDMA) signals from different UEs. While small timing errors can be corrected for by using known signal processing techniques that exploit the OFDM cyclic prefix, larger timing differences between UEs can lead to unrecoverable overlap between the subcarriers causing significant performance degradation.
The requirement for tight timing control for uplink access leads to significant overhead both in terms of signaling and eNB processing load. For example, a UE in Idle mode or a UE that has no valid timing advance has to first transmit a RACH preamble and receive an acknowledgement with the associated timing advance and grant before it can transmit any information to the network. While this overhead may be justified when connections are relatively long-lasting (i.e., when a substantial amount of data will be transmitted uplink over the connection), it may not be justified when the connection is used to transmit a very small amount of data, as is the case for many new applications, such as machine-to-machine (M2M) applications.